Audiometers



ay 29, 1962 CARL-AXEL E. TEGNER ETAL 3,037,082

AUDIOMETEJRS 2 Sheets-Sheet 1 Filed Dec. 10, 1958 RUBBER FIG! 6 050. AME

INTERRUPTER May 29, 1962 Filed Dec. 10, 1958 2 Sheets-Sheet 2 26 all IUnited States Patent 3,037,082 AUDIOMETERS Carl-Axel Elof Tegnr, BirgerJarlsgatan 33, Stockholm,

Sweden, and Henry Anderson, Konstgjutarvagen 48,

Johanneshov, Sweden Filed Dec. 10, 1958, Ser. No. 779,417 Claimspriority, application Sweden Mar. 31, 1958 3 Claims. (Cl. 179-1) Thisinvention relates to an audiometer or apparatus for determining thethreshold values of human hearing.

In known designs the electrical parts of the audiometer comprise anoscillator with at least one amplifying stage and an attenuation set.The audio-meter can be connected either to the mains of an electricalsupply system or to batteries. A cord connects the apparatus to areceiver which is applied to the patients car by means of a headband.The measuring is effected by adjusting the audiometer to emit a tone ofa selected frequency and subsequently transmitting to the patient toneimpulses of varying intensity and having a duration of about .onesecond. Then the same test is performed with tones of other frequencies.When the patient perceives these tone impulses in his receiver hesignals to the operator, and the operator then can ascertain thepatients threshold values for the different frequencies. The impulsesare generated by operating a switch, called an interrupter, which ,opensand closes an electric oscillator circuit. The measuring is based on thecondition that the patient will signal to the operator when he perceivesthe actual tone and not when he hears a click, a sliding frequency, orsome other form of distortion of the tone, and the degree of permissibledistortion as well as the time for the intonation and/or fading of thetone have been determined by international standards.

An interrupter which meets the demands of such standards can be designedin several ways. When an LC-oscillator is used, the impulses usually arederived by interrupting the anode voltage circuit of the oscillatortube. If an RC-oscillator or beat-frequency oscillator is used, the tonecircuit is usually interrupted by blocking one of the amplifying stageswhich follow after the oscillator.

All known solutions of the interrupter problem entail complicated andexpensive constructions, and, in addition, it is a disadvantage that noappreciable reduction of the consumption of current is obtained in thepauses when no tone impulse is emitted by the audiometer. In anaudiometer supplied from the mains of a power-supply the current drainis of little importance, but in a batterydriven audiometer the currentdrain is an important factor since the size of the audiometer is largelydependent on the size of the battery or batteries. A measurement ofhearing usually takes at least 20 minutes. During this period 100 to 120impulses are emitted, each having a duration of about one second, thatis to say, the audiometer emits a tone impulse during slightly less thana tenth of the time for measuring the hearing.

The main object of the present invention is to eliminate thesedisadvantages by connecting the interrupter in the oscillator circuit inseries between the source of current and the oscillator.

A further object of the invention is to make the interrupter in itselffree from distortion when connected in a transistor circuit and torender the interrupter adaptable to standard time constants. In this waythe interrupter may have a simple and inexpensive construction.

A still further object is to provide an audiometer which consumescurrent when the impulses are emitted only, but not in the pauses,whereby the current drain of the audiometer will be reduced to aminimum. In this way the current may, for example, be reduced to lessthan a tenth compared with known constructions of similar type.

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In all audiometers the interrupters comprise a resilient contact memberand the tone is interrupted in the resting or inactive position of thiscontact member. according to our construction an interruption of thetone is caused by an interruption of the current supply circuit, it is afurther object of the invention to prevent the audiometer from remainingconnected to the current supply by an oversight, which often happenswith battery-driven apparatus of this type. One reason for this fault isthat it is not possible to use a warning lamp indicating when thecurrent supply is connected, since this lamp would consume more currentthan the Whole audiometer.

A still further advantage of the invention is that the reduced currentdrain facilitates the use of small batteries. Also the overalldimensions of the audiometer may be reduced considerably, which is mostdesirable from practical point of view. In the construction according tothe invention the oscillator and the amplifier units, together with thesource of cur-rent and the operating or control means may be builttogether in a common casing which is small enough to be mounted directlyon the receiver so that the operator, when making tests, can hold theentire set in his hand and press it against the patients ear.

One embodiment of the audiometer according to our invention isillustrated as an example on the accompanying drawing, in which FIG. 1shows the audiometer in longitudinal section,

FIG. 2 shows a top view of the audiometer,

FIG. 3 is a cross section on the line IIIIII in FIG. 1, and

FIG. 4 is a diagram of the electrical circuits of the audiometer.

In the embodiment shown in the drawing the audiometer comprises a casing11 having at one end a receiver provided with a rubber cushion 9 forinstance, which is held against the ear of the patient during thetesting. The receiver has a central aperture 12 through which the soundfrom a conventional telephone cap 8 with a diaphragm may penetrate intothe ear of the patient. The top 14 and the bottom 17 of the casing 11are interconnected by means of rods 18, holding the top 14 and thebottom 17 together. Within the casing 11 there is also arranged abattery box 4 secured to the top 14 of the casing 11 and closed by ascrew cap 10. The box 4 encloses a battery 15 which supplies a toneoscillator 6 comprising an amplifier with transistors. One terminal 15aof the battery 15 contactsa fixed contact 16 connected to other elementsof the circuit in a manner to be described with reference to FIG. 4, andthe other terminal of the battery 15 contacts the metallic part of thetop 14 which is conductively connected to certain elements of thecircuits.

The oscillator 6 is of known design and need not be described. It isconnected electrically to the telephone cap 8. The oscillator amplifier6 is also connected to an attenuator set 3, a frequency switch 5 and aninterrupter 7, which is connected in the circuit between the battery 15and the oscillator amplifier 6. The interrupter 7 comprises a switchwith one fixed and one resilient contact member, said members beingbrought into electrical contact with one another to close the circuit onoperating the interrupter with the hand or finger of the operator. Theattenuator set 3 is used for adjusting the intensity of sound by meansof a knob 1, graded in decibels of loss of hearing. For adjusting thepitch of sound the frequency switch 5 is set by a knob 2, graded incycles per second.

To enable operation with one hand each of the rotatable knobs 1 and 2may be fitted with a projecting wing or flap 1a and 20, respectively, tofacilitate operation with the fingers of the operator.

FIG. 4 shows that the interrupter 7 is connected in series between thebattery 15 (2.6 volts) and a choke coil Since,

20, intended to eliminate the occurrence of clicks on breaking thecircuit. Shunted across the choke coil and the battery is anelectrolytic condenser 21 (50 mf.). The choke coil is connected to acircuit including the receiver 22 and a change-over switch comprising amovable contact arm 23 which may be moved so as to contact a number offixed contacts 24, and 26 in succession, thereby varying the intensityof the emitted tone. Each fixed contact 24, 25, 26 respectively, isconnected to a resistance 24a (2.5 ohms), 25a (24 ohms) and 26a (500ohms) respectively.

In this way the intensity of the tone received in the receiver 22 willbe varied. The contact position 24 corresponds to a value of 20decibels, for instance, contact position 25 to a value of 40 decibels,and contact position 26 to a value of 60 decibels on the scale of theknob 1 in FIG. 1. Of course the invention is not restricted to these orother numerical values appearing in this specification, which arementioned as examples only.

The amplifier circuit includes a transistor 27 connected to a resistance28 (1 kiloohm) and an electrolytic condenser 29 (50 mt.) which has thepurpose of supplying a predetermined base current to the transistor. Aresistance 30 (20 kilo-ohms) is connected between the resistance 26a andthe transistor 27.

A further transistor 31 is connected in the oscillator circuit and aresistance 33 (100 kilo-ohms) and a condenser 32 (0.04 mf.) areconnected in series between the two transistors 31 and 27. For thecontrol of the volume there is arranged a switch device comprising acontact arm 34 which can be moved to contact one of a plurality of fixedcontacts 35, 36 and 37 in succession, each connected to a calibrationresistance, 35a, 36a and 37a, respectively, calibrated to the valuewhich gives the specified tone intensity for the frequency used.

38 is an oscillator coil from which different frequencies may bederived, by means of a switching device comprising interconnectedmovable contact arms 39, 40, and a plurality of fixed contacts 41, 42,43 and 4 45, 46 respectively. Contacts 41, 42 and 43 are connected todifferent tap points of the coil 38. Contacts '44, 45, 46 are eachconnected to a condenser 47 (0.01 mf.), 48 (0.2 Inf.) and 49 (0.18 mi.)respectively. Contacts 44 and 45 are also connected to a resistance 50(5 kilo-ohms) and 51 (2 kilo-ohms) respectively. The contact arms 39,are interconnected mechanically to contact arm 34 so that they will movetogether, the result being that the frequency will be varied from 4,000cycles/see, for instance (contacts 41, 46), to, say, 1,000 cycles/sec.(contacts 42, 45) and to 250 cycles/see, for instance (contacts 43, 44).Other frequencies may be used and if desired one sole frequency (ofinstance 4,000 cycles/sec.) may be used, or two frequencies (forinstance 2,000 and 4,000 cycles/sec.) may be used.

52, 53 and 54 are further resistances having a value of 26 kilo-ohms,1.6 kilo-ohms and 2 kilo-ohms respectively.

While we have illustrated and described the preferred form ofconstruction for carrying the invention into eifect, this is capable ofvariation or modification without departing from the spirit of theinvention. We therefore do not wish to be limited to the precise detailsdisclosed but desire to avail ourselves of such variations ormodifications as fall within the scope of the appended claims.

What we claim is:

1. An audiometer comprising an audio frequency oscillator and anamplifier connected to the oscillator output and comprised of electronicvalves in the form of transistors, a speaker connected to the output ofsaid amplifier, a source of current for supplying electrical energy tosaid oscillator and said amplifier, an interrupter connected in seriesbetween said source of current and said oscillator and amplifier, forinterrupting the total current supply to said oscillator and amplifier,said interrupter having a manually operable actuating member, filteringmeans in the form of a choke connected in a series circuit with thecurrent supply and switch and a capacitor shunting said series circuitfor smoothing out the transients caused by the interrupter, when saidcurrent supply is closed or interrupted.

2. An audiometer according to claim 1, wherein said speaker, oscillator,interrupter and source of current are assembled in a casing so as toform one single unit that the operator can hold at the ear of thepatient when making the test.

3. An audiometer according to claim 1, wherein said actuating member ofsaid interrupter comprises a pushbutton in easy reach of one of theoperators fingers when he holds said casing in his hand, saidpush-button being spring actuated for restoring it to its non-actuatedposition.

References Cited in the file of this patent UNITED STATES PATENTS

